Feasibility of stocking to enhance flathead fisheries Recreational Fishing Grants Program Research Report Feasibility of stocking to enhance flathead fisheries January 2019 Recreational Fishing Grants Program Research Report Published by the Victorian Government, Victorian Fisheries Authority (VFA), January 2019 © The State of Victoria, Victorian Fisheries Authority, Melbourne 2019 This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968 . Authorised by the Victorian Government, 1 Spring Street, Melbourne. Preferred way to cite this publication: Ingram, B.A. (2019) Feasibility of stocking to enhance flathead fisheries. Recreation Fishing Grants Program Research Report. ISBN 978-1-76090-063-2 (print) ISBN 978-1-76090-064-9 (pdf/online/MS word) Author Contact details: Dr Brett Ingram Fisheries Management and Science Branch, Victorian Fisheries Authority Private Bag 20, Alexandra, Vic 3714. 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Call us via the National Relay Service on 133 677 or visit www.relayservice.com.au Feasibility of stocking to enhance flathead fisheries ••• Recreational Fishing Grants Program ii Contents Executive summary ____________________________________________________________________ 1 Introduction ___________________________________________________________________________ 3 Stock enhancement ____________________________________________________________________ 4 Marine stock enhancement 5 Stock enhancement in Victoria 5 Biology and current status of important Victorian flathead stocks in Victoria ____________________ 6 Hatchery production of flathead fingerlings ________________________________________________ 9 Broodstock 9 Spawning 9 Egg incubation and rearing larvae 11 Fry rearing (nursery culture) 11 Diseases and health management 12 Nutrition 12 Options for supply of juvenile flathead for stocking 12 Review of previous flathead stocking programs ___________________________________________ 14 Stocking flathead in Victorian waters _____________________________________________________ 17 Stocking dusky flathead in eastern Victoria 17 Stocking sand flathead in Port Phillip Bay and Corio Bay 19 Conclusions and recommendations ______________________________________________________ 21 Where to from here 22 Acknowledgements ___________________________________________________________________ 23 References __________________________________________________________________________ 24 Appendix I. Stockings of coastal, estuarine and marine species into Victorian waters ___________ 28 Appendix II. Flathead species summary descriptions _______________________________________ 29 Appendix III. Flathead growth parameters ________________________________________________ 31 Appendix IV. Fish hatcheries in south-eastern Australia with the potential to breed flathead ______ 32 Appendix V. Estuaries, inlets, bays and coastal lagoons of Victoria, and their potential for stocking with flathead _________________________________________________________________________ 34 Feasibility of stocking to enhance flathead fisheries ••• Recreational Fishing Grants Program iii Executive summary Several species of flathead are very important and highly popular species targeted by recreational anglers fishing bays and inlets across Victoria. Stocks of some species, however, have declined significantly in recent decades which has become a key issue for both The Victorian Fisheries Authority (VFA) and stakeholders. Stocking hatchery-bred fish occurs globally in freshwater, estuarine and marine environments to replenish, maintain or enhance populations. Stocking is used by fisheries managers to restore depleted populations of recreationally and commercially significant fish species, and may be a potential management option to ameliorate impacts of prolonged recruitment failure in some flathead stocks. The objective of this study was to determine the feasibility of establishing a program for stocking hatchery-bred flathead fingerlings to recover and enhance flathead stocks in selected estuaries, bays and coastal lagoons of Victoria. The study aimed to identify the need, constraints and opportunities for stocking flathead into Victorian waters, review available information on techniques and resources required to breed flathead in captivity and review previous flathead stocking programs. Previous studies have indicated there is interest from stakeholders in stocking flathead into selected water to recover stocks and enhance fisheries, particularly dusky flathead on the east coast and sand flathead to the west. There is a considerable amount of information on the biology and ecology of flathead that will assist in developing captive breeding techniques for target species, such as size at maturity, spawning season and habitat, fecundity and larval growth. Techniques for hatchery production of dusky flathead fingerlings have already been developed. Hatchery facilities for production of flathead require access to good quality filtered seawater, tanks for holding broodstock, eggs and larvae, large ponds for growth of fry, and facilities for culturing food species (rotifers and brine shrimp). These techniques may be adapted for breeding other flathead species. There have been concerns about the status of some stocks of flathead in Victoria. Sand flathead in PPB have exhibited sustained limited recruitment over the last 20 years. There is some uncertainty regarding declining catch rates of some dusky flathead fisheries on the east coast. Stocking is one option for managing fish stocks, particularly where recruitment is limited. Stocking programs release juveniles produced in captivity (hatcheries) on a regular basis to conserve, restore or enhance fisheries. This approach can have a range of benefits including the recovery threatened species and stocks that have been depleted and increase yields in fisheries that are below the carry capacity of the environment. Stocking programs also require access to sufficient numbers of juveniles of appropriate species and stock (genetic structure) that will survive and growth after release and remain in the area to enter the fishery. Several estuaries, inlets, bays and coastal lagoons in Victoria that may be considered for stocking with flathead were identified in this report. However, not all stocking programs are successful. While some have increased yields and generated economic and social benefits, others have either failed to live up to expectations, or their effectiveness have not, or could not be, assessed. For example, there has only been one flathead stocking trial program in Australia. During a 3-year project conducted between 1996 and 1997; 100,000 juvenile dusky flathead were released in the Maroochy River, QLD, as a pilot project and partly to recover stocks following a fish kill. Although stocked dusky flathead first appeared in fishery independent surveys five months after release, representing, and were detected in both recreational and commercial fisheries, assessments failed to detect a significant change in the size of the population and an economic assessment was unfavourable. Consequently, a responsible approach to stocking, with well-defined management objectives and rationale for stocking, and plans for their monitoring and evaluation, is promoted by fisheries scientists and managers. Flathead species are considered as potential candidates for stocking Victorian estuaries because: • They are a highly popular recreational angling species. • Some stocks may need supplementation to overcome periods when recruitment is limited. • They are relatively sedentary and so are less likely to move away from the area stocked. • They can be bred in captivity. This report has indicated that it is feasible to produce juvenile flathead for stocking and that there are a number of waters that may be considered for enhancing with hatchery-bred fish. For stocking to occur there is a need to: 1. Determine the need and objectives, which should consider cost, angler demand, expected returns & environmental suitability. This should involve stakeholders in the planning process, and assess the potential contribution of releases as well as alternative options for achieving the goals of fisheries management objectives for the fishery. Feasibility of stocking to enhance flathead fisheries ••• Recreational Fishing Grants Program 1 2. Identify estuaries requiring enhancement by stocking, such as where there is sustained limited recruitment. This will require knowledge of the abundance and level of recruitment of stocks within these estuaries. 3. Estimate carrying capacity (productivity) of the environment to determine the level of stocking needed for recovery within the carrying capacity of the water. 4. Determine genetic structure of Victorian flathead stocks to ensure